Method of making an extended surface double wall tubing from strip stock



July 21, 1970 E. P. HABDAS 3,521,537

METHOD OF MAKING AN EXTENDED SURFACE DOUBLE WALL TUBING FROM STRIP STOCK Original Filed Jan. 2, 1968 2 5heets sheet l FIG.5

- v INVENTOR EDWARD P. HABDAS y .i LY/j ut 2 3 ATTORNEYS v July-21, '1970 E. P. HABDAS 3,521,537

METHOD OF MAKING AN EXTENDED SURFACE DOUBLE WALL TUBING FROM STRIP STOCK Original Filed Jan. 2. 1968 2 Sheets-Sheet 2 .FIGJS V r INVENTOR EDWA D P. HABDAS ATTORNEYS United States Patent O U.S. Cl. 113-118 Claims ABSTRACT OF THE DISCLOSURE The method of making finned tubing formed from strip having one edge slotted to provide fins, the strip being rolled into tubular configuration and the strips twisted through 90 degrees and wrapped around and attached to the outer surface of the tubing.

CROSS-REFERENCE TO RELATED APPLICATION The present application is a division of my prior copending application, Ser. No. 695,098, filed Jan. 2, 1968.

BACKGROUND OF THE INVENTION The invention relates to the field of heat exchange tubing in which the outer surface of the tubing is extended as for example by the provision of circular or helically extending fins. Fins have in some instances been separately formed and wrapped around and brazed or otherwise secured to the outer surface of plain tubing. Another practice has been to form circular or helical fins by rolling the fins out of the material of the tubing by opposed fin forming rolls.

In addition, tubing without extended outer surface has been formed by rolling strip material into double wall tubing in which the strip material is brazed to produce in effect, solid tubing,

SUMMARY OF THE INVENTION In accordance with the present invention strip material having a width equal approximately to three times the circumference of the desired tubing is provided along one edge with a multiplicity of parallel slits extending approximately one-third of the way across the strip. The material between the slits is then rotated through 90 degrees so as to present the width of the finning elements thus formed in a plane perpendicular to the plane of the strip material. Thereafter, the strip is rolled so as to form a double wall tube which will cause the tube to occupy a location at the inner or connected ends of the fin forming elements. These elements are then wrapped around the tubing to form either a multiplicity of axially spaced circumferential fins, or if preferred, each fin may be given a slight lead so that all of the fins together extend at a helical angle. In the latter case the fins may be somewhat longer than otherwise and may be disposed to provide helical fins having one, two or more starts.

The interconnection between the adjacent surfaces of the tube convolutions may be brazed together by the provision of brazing material and the inner edges of the fins may likewise be brazed to the outer surface of the double wall tube. If the tubing is copper clad steel for example, the copper coating will supply the brazing material to bond the walls of the double wall tubing together and also to bond the inner edge of the fins to the tubing.

It is accordingly an object of the present invention to provide a method of making extended surface tubing comprising the steps of slitting one edge of an elongated strip to provide fin forming portions, wrapping or rolling 3,521,587 Patented July 21, 1970 "ice the unslitted portion of the strip into tubular configuration, twisting the fin elements through degrees to present an edge surface thereof for attachment to the tubing, wrapping the finning elements around the tubing, and bonding the convolutions of the strip together to form integral tubing and bonding the inner edges of the fins to the outer surface of the tubing.

Other objects and features of the invention will be come apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of extended surface tubing constructed in accordance with the present invention.

FIG. 2 is an end view of the tubing shown in FIG. 1.

FIG. 3 is a fragmentary elevational view of a portion of the strip from which the tubing is made.

FIG. 4 is an end view of the strip seen in FIG. 3.

FIG. 5 is a fragmentary elevational view of the strip provided with fin forming slits.

FIG. 6 is an end view of the slitted strip shown in FIG. 5.

FIG. 7 is a fragmentary elevational view of the slitted strip of FIG. 5, with the fin elements twisted through 90 degrees.

FIG. 8 is an end view of the strip shown in FIG. 7.

FIG. 9 is an end view of tubing formed by rolling the unslitted portion of the strip into a tube, the figure being on a substantially enlarged scale.

FIG. 10 is a side elevational view of the structure shown in FIG. 9.

FIG. 11 is a view similar to FIG. 9, showing the fin elements wrapped around the tubing and bonded thereto.

FIG. 12 is a side view of the structure shown in FIG. 11.

FIG. 13 is a fragmentary elevational view of tubing in which the fin structure is helical.

FIG. 14 is a fragmentary view showing the ends of the fin forming portions inclined.

FIG. 15 is an end view showing finned tubing constructed from the slitted material of FIG. 14.

DETAILED DESCRIPTION The extended surface tubing shown in FIG. 1 comprises a tube proper indicated at 10 formed of an inner convolution 12 and an outer convolution 14, and generally radially extending fin structure 16.

In order to produce a finned tube of this character from a single strip of stock, a method as sequentially illustrated in FIGS. 3-12 is provided. The starting material is an elongated strip 20 formed of metal such for example as copper clad steel, the strip having a transverse width W equal approximately to three times the desired diameter of the tubing 10. As shown in the figures, the tubing is constituted by three longitudinally extended zones each designated #1) where D represents the approximate diameter of the finishing tubing.

The first step in the production of the extended surface tubing in accordance with the present invention is to provide longitudinally extending slits 22 which extend approximately one-third of the way across the strip 20. The slits 22 define therebetween fin forming portions 24 and the spacing of adjacent slits determines the height of the fins as provided on the finished structure. It will be apparent as the description proceeds that an increase in spacing between the slits not only results in an increase in fin height, but it results also in a corresponding increase in spacing between adjacent fin convolutions.

The next step in the production of fined tubing in accordance with the present invention involves the twisting of each of the fin forming portions or elements 24 through 90 degrees so as to present an edge surface 26 of the fin forming elements parallel to the plane of the strip for engagement therewith, as will subsequently appear.

After the fins have been twisted into the relationship illustrated in FIG. 8, the strip 20 is rolled or wrapped into a double wall tube indicated at 28, the tube having an inner convolution 30 and an outer convolution 32. It the strip 20 is copper clad steel, the copper cladding constitutes brazing material which will unite the abutting surfaces of the inner and outer convolutions 30 and 32 as well as provide bonding material for the fin forming portions 24, as will subsequently appear.

Finally, the individual fin forming elements 24 are now wrapped around the tube 28 to bring the edge surface 26 thereof into engagement with the outer surface of the outer tube convolution 32, as best seen in FIG. 11. It is appreciated that the fin forming portions 24 may offer substantial resistance to bending in the plane illustrated in the figures so that it may require lateral support against buckling. This of course varies in accordance with the height of the fin, the tendency to buckling and the resistance to bending being more pronounced as the height of fin increases.

It is within the contemplation of the present invention to permit some limited buckling of the inner edge of the fin to allow for the difference in circumference between its inner edge 26 and its outer edge 34. Alternatively, the wrapping of the fin into the configuration illustrated in FIG. 11 may be permitted by some stretching and thinning of the fin material adjacent its outer periphery.

In any case, the assembly as shown in FIG. 12 may be completed simply by retaining the slitted and wrapped strip in the required configuration and subjecting it to heat so as to melt the copper coating and effecting a brazed bonding of the inner and outer convolutions of the tubing to each other.

While the fins as illustrated in the figures are bent into individual circumferentially extending convolutions, it will be appreciated that each fin may if desired be caused to extend at a helix so as to be adjacent to the start of the next succeeding fin whereby all of the fin forming elements are caused to occupy substantially a single helical path. Alternatively, if each of the fin forming elements is wrapped around the tubing so as to bring its free end into a position contiguous to the second fin forming element rather than the next adjacent fin formend of the fin or of the adjacent fins as the case may be, leaving a triangular shaped gap. If desired, the slitting operation may be accompanied with a cutting operation to provide inclined ends 50 so that when the strip is rolled up into a tube and the individual fins are wrapped around the tube, the end 50 of each fin is closely adjacent to the opposite end of the fin, thus eliminating the presence of the triangular gap as shown in the previous embodiments of the invention.

What I claim as my invention is:

1. The method of making finned tubing which comprises slitting one edge of an elongated strip transverse ly part-way across the strip to define a plurality of fin forming elements, twisting the fin forming elements through degrees, rolling the unslitted portion of the tubing into tubular configuration terminating substantially at the inner edge of the slits, thereafter wrapping the fin forming elements around the tube, and bonding together rolled portions of the unslitted strip and bonding the edges of the fin forming elements to the tube.

2. The method of claim 1 which comprises slitting the strip substantially one-third of the distance transversely of the strip, and rolling the unslitted portion of the strip into tubing of double wall thickness having inner and outer convolutions.

3. The method as defined in claim 1 which comprises wrapping the individual fin forming elements so that the free end of each element is brought into position contiguous to the attached end thereof to produce a multiplicity of essentially circular fins.

4. The method as defined in claim 1 which comprises wrapping each fin forming element into a helical convolution so that the free end thereof is brought into position contiguous to the connected end of an adjacent fin forming element.

5. The method as defined in claim 4 which comprises forming the slitted strip from copper clad steel, and in which the final bonding operation is a brazing operation in which the copper cladding serves as the brazing material for attaching the inner convolution to the outer convolution of the tube and for attaching the inner edge of each fin to the outer surface of the outer convolution.

References Cited UNITED STATES PATENTS 754,195 3/ 1904- Bullard. 1,608,905 11/1926 Murray et al. 2,372,795- 4/1945 Rodeck 113--1l8 2,400,737 5/1946 Brown. 2,537,797 l/l951 Simpelaar 184 X 3,288,209 11/ 1966 Wall et al. l65-184 3,362,058 1/1968 Morris et al. 29--l57.3

CHARLIE T. MOON, Primary Examiner D. C. REILEY, Assistant Examiner US. Cl. X.R. 29--157.3 

